JP2005297557A - Inkjet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stable ejection even when the frequency of a driving pulse applied to a piezoelectric element and the temperature environment in which the head is used are various.
A ratio of a flow path resistance Ra of a throttle portion disposed between an ink chamber and a pressure chamber and a flow path resistance Rb of a nozzle is 0.48 to 1.26, more preferably 0.8 to 1. 0.
[Selection] Figure 9

Description

  The present invention relates to an inkjet head that performs recording by discharging ink onto a recording medium. More specifically, a narrowed portion having a narrower flow path than a pressure chamber is formed between an ink chamber and a pressure chamber, and the piezoelectric head The present invention relates to an inkjet head that applies pressure to ink in a pressure chamber by a method and ejects ink from nozzles.

  As an ink jet head used for an ink jet printer or the like, an ink chamber for containing ink, a pressure chamber to which ink is supplied from the ink chamber, a nozzle communicating with the pressure chamber, and the like are formed, and pressure is applied to the ink in the pressure chamber. In some cases, ink is ejected from the nozzles. In such a head, there is a technique in which a piezoelectric element is disposed on a pressure chamber, and the piezoelectric element is deformed by applying a driving pulse, thereby changing the volume of the pressure chamber and applying pressure to ink in the pressure chamber. Are known.

In recent years, high-speed and high-quality printing has been demanded, and various techniques for realizing this have been proposed. For example, in the ink jet head having the above configuration, paying attention to the flow path resistance of the entire ink flow path and the flow path resistance of the throttle formed between the ink chamber and the pressure chamber, the ratio of these flow path resistances is set within a predetermined range. Thus, there is a technique for preventing ejection stability from being impaired even when high-speed printing is performed (see Patent Document 1).
JP 2003-19796 A

  However, today, printing speed and image quality are further improved, and it is desired to develop an ink jet head that can cope with higher speed and image quality. In the inkjet head having the above-described configuration, it is particularly required that stable ejection can be realized even when the frequency of the driving pulse applied to the piezoelectric element and the temperature environment in which the head is used are various.

  An object of the present invention is to provide an ink jet head capable of realizing stable ejection even when the frequency of a driving pulse applied to a piezoelectric element and the temperature environment in which the head is used are various.

Means and effects for solving the problems

  The inventor conducted experiments under various conditions, and the configuration of the throttle portion and the nozzle was greatly related to the discharge stability, and the ratio between the flow resistance of the throttle and the flow resistance of the nozzle was set within a predetermined range. It was confirmed that the above purpose could be achieved.

  The ink jet head of the present invention is disposed on an ink chamber for containing ink, a pressure chamber to which ink is supplied from the ink chamber, and the pressure chamber, and applies pressure to the ink in the pressure chamber by applying a drive pulse. The pressure applying means for providing fluctuation, and the ink chamber and the pressure chamber are disposed between the throttle chamber having a narrower flow path than the pressure chamber and the pressure chamber. A nozzle that ejects ink in accordance with a change in volume, and a ratio Ra / Rb of the flow path resistance Ra of the throttle portion to the flow path resistance Rb of the nozzle is 0.48 to 1.26.

  According to the above configuration, since the ratio of the flow path resistance Ra of the throttle portion and the flow path resistance Rb of the nozzle is in the predetermined range, the frequency of the driving pulse applied to the piezoelectric element and the temperature environment in which the head is used are various. Even so, stable ejection can be realized.

  In the inkjet head according to the aspect of the invention, it is preferable that the pressure applying unit is a piezoelectric element that is deformed by application of the driving pulse to change the volume of the pressure chamber.

  According to the above configuration, since the pressure fluctuation can be given to the ink by the change in the volume of the pressure chamber, the pressure fluctuation can be accurately given at a desired timing.

  In the ink jet head of the present invention, the piezoelectric element is deformed so as to increase the volume of the pressure chamber when the drive pulse is applied, and the volume of the pressure chamber is restored when the drive pulse is applied. It is preferable to be deformed.

  According to the above configuration, the application time of the drive pulse is appropriately set, and the negative pressure wave generated by the increase in the pressure chamber volume is reduced and reflected at the timing when the negative pressure wave is reflected back to the positive pressure wave. A positive pressure wave generated by reducing the volume of the pressure chamber and a positive pressure wave reflected and reflected from the pressure wave can be applied to the ink in the pressure chamber.

  In the inkjet head according to the aspect of the invention, it is preferable that a ratio Ra / Rb of the flow path resistance Ra of the narrowed portion and the flow path resistance Rb of the nozzle is 0.8 to 1.0.

  According to the above configuration, even when a design error occurs, the temperature is outside the set temperature for use, or other various problems occur, the discharge stability can be maintained well.

    In the ink jet head of the present invention, it is preferable that the frequency of the driving pulse is 5 to 96 kHz.

  This is because the effect of the present invention can be reliably obtained by setting the ratio of the flow path resistance Ra of the throttle portion to the flow path resistance Rb of the nozzle within the predetermined range, particularly in the range of the frequency of the drive pulse of 5 to 96 kHz. Because it is done.

  Moreover, in the inkjet head of this invention, it is preferable that the said aperture | diaphragm | squeeze part is formed by half etching.

  According to the above configuration, the throttle portion having the predetermined flow path resistance Ra can be formed efficiently at low cost.

  The inkjet head of the present invention is configured by laminating a plurality of plate-like materials, and the ink chamber, the pressure chamber, the throttle portion, and the nozzle are any one of the plurality of plate-like materials. Preferably it is formed.

  According to the above configuration, the ink chamber, the pressure chamber, the nozzle, and the throttle portion can be easily formed. In particular, the throttle portion and the nozzle having the predetermined flow path resistances Ra and Rb can be formed inexpensively and efficiently.

  Furthermore, in the ink jet head of the present invention, it is preferable that the narrowed portion is formed by half etching on the same plate-like material on which the pressure chamber is formed.

  According to the above configuration, the throttle portion having the predetermined flow path resistance Ra can be formed more inexpensively and efficiently.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  First, an overall configuration of an ink jet head according to an embodiment of the present invention will be described with reference to FIG. The ink jet head 101 of this embodiment is used in an ink jet printer that performs recording by discharging ink onto a conveyed paper (recording medium), and an actuator unit 2 is bonded onto a flow path unit 1. Further, a flexible printed wiring board (FPC) 40 is joined on the actuator unit 2. The FPC 40 is connected to a controller (not shown) that performs overall control of the inkjet head 101, and transmits a drive signal output from the controller to the actuator unit 2.

  Here, the flow path unit 1 will be described in detail with reference to FIGS. 2 and 3.

  The flow path unit 1 is configured by laminating a total of five plate-like materials including a cavity plate 3, a base plate 4, manifold plates 6 and 7, and a nozzle plate 9. Each plate 3, 4, 6, 7, 9 is made of a 42% nickel alloy steel plate having a substantially rectangular shape and a thickness of 50 μm to 150 μm, and has a large number of openings or recesses formed by pressing or etching, These openings or recesses are joined to each other by an adhesive applied to each planar region so as to communicate with each other.

  A large number of pressure chambers 11 are drilled in the cavity plate 3 in two rows on both sides across a center line along the longitudinal direction thereof. Each pressure chamber 11 is formed by pressing so as to penetrate in the plate thickness direction of the cavity plate 3, and has a substantially rectangular shape in plan view, and is arranged so that its longitudinal direction is parallel to the short direction of the cavity plate 3. ing. When reference lines 3x and 3y (see FIG. 3) parallel to the center line along the longitudinal direction of the cavity plate 3 are set, one end in the longitudinal direction of the pressure chamber 11 included in the column on the left side of the center line is One end in the longitudinal direction of the pressure chambers 11 included in the column on the right side of the center line is disposed along the reference line 3x on the left side of the center line. In addition, the longitudinal centerlines of the pressure chambers 11 included in each row are arranged alternately. That is, the pressure chambers 11 are arranged in a staggered manner.

  As shown in FIG. 3, one end 11 a on the center side of the cavity plate 3 in each pressure chamber 11 passes through micro-diameter holes 12 a, 12 b, and 12 c that are formed in a staggered manner in the base plate 4 and the manifold plates 6 and 7, respectively. The nozzle plate 9 communicates with nozzles 10 that are similarly perforated in a zigzag manner. On the other hand, the other end of each pressure chamber 11 is provided through a narrowed portion 11 b and a recessed portion 11 c that are recessed by half etching so as to open only on the lower surface side of the cavity plate 3, and a hole 13 formed in the base plate 4. The manifold plates 6 and 7 are communicated with manifolds 6a and 7a, 6b and 7b.

  As shown in FIG. 3, the throttle portion 11 b has a width smaller than the width of the pressure chamber 11, and is formed so that the flow path is narrower than the pressure chamber 11. As will be described in detail later, the ratio Ra / Rb of the flow path resistance Ra of the throttle portion 11b to the flow path resistance Rb of the nozzle 10 is 0.48 to 1.26, preferably 0.63 to 1.05, more preferably. Is 0.8 to 1.0. Here, since the narrowed portion 11b is formed by half etching as described above, the narrowed portion 11b having the predetermined flow path resistance Ra can be formed at low cost and efficiently.

  As shown in FIG. 2, an elliptical recess 17 elongated in the short direction of the cavity plate 3 in plan view is formed near one end in the longitudinal direction of the cavity plate 3. Two ink supply holes 15 a and 15 b aligned in the short direction of the cavity plate 3 are formed at the bottom of the recess 17. A filter (not shown) for removing dust in the ink supplied from an ink tank (not shown) is stretched on the upper surface of each ink supply hole 15a, 15b.

  The base plate 4 is provided with a large number of holes 12a in two rows on both sides across a center line along the longitudinal direction. The holes 12a are arranged in a staggered manner, like the pressure chambers 11 described above. In the vicinity of both ends in the short direction of the base plate 4, a large number of holes 13 are formed in a row along the longitudinal direction. In the base plate 4, two ink supply holes 16 a and 16 b that are slightly larger than the ink supply holes 15 a and 15 b are formed at positions corresponding to the ink supply holes 15 a and 15 b of the cavity plate 3.

  The manifold plate 6 is provided with a plurality of holes 12b corresponding to the holes 12a formed in the base plate 4 in two rows on both sides across the center line along the longitudinal direction. Further, manifolds 6a and 6b are formed in the vicinity of both sides in the short direction of the manifold plate 6 so as to extend along the longitudinal direction.

  The manifold plate 7 has the same hole 12c as the hole 12b formed in the manifold plate 6, and the same position and plane shape as the manifolds 6a and 6b formed in the manifold plate 6, and the upper surface side of the manifold plate 7 Manifolds 7a and 7b are formed by recessing by half etching so as to open only at.

  One end of each of the manifolds 6a and 7a is disposed at a position overlapping the ink supply hole 16a of the base plate 4 in a plan view. Similarly, one end of each of the manifolds 6b and 7b is disposed at a position overlapping with the ink supply hole 16b of the base plate 4 in a plan view. ing. The manifolds 6 a, 7 a, 6 b, 7 b extend so as to include regions corresponding to the respective rows of the two rows of holes 13 formed in the base plate 4. The manifold plates 6 and 7 are overlapped and joined to form manifolds 6a, 7a, 6b, and 7b as ink chambers (see FIG. 4).

  As shown in FIG. 2, nozzles 10 are formed in the nozzle plate 9 at positions corresponding to the respective holes 12 c formed in the manifold plate 7. The nozzle 10 is formed in a tapered shape that gradually becomes smaller in diameter in the ejection direction in which ink is ejected by performing excimer laser processing on a substrate such as polyimide, for example (see FIG. 7).

  The ink supplied from the ink tank (not shown) to the ink supply holes 15a and 15b of the cavity plate 3 passes through the ink supply holes 16a and 16b formed in the base plate 4 and the left and right manifolds 6a, 7a, 6b, Flows into 7b. The ink that has flowed into the manifolds 6a, 7a, 6b, and 7b has a hole 13 formed in the base plate 4, a concave portion 11c and a throttle portion 11b formed at the other end of each pressure chamber 11 (see FIGS. 3 and 4 for both). It distributes in each pressure chamber 11 via. The ink in each pressure chamber 11 reaches from the one end 11a thereof to the nozzle 10 formed in the nozzle plate 10 through holes 12a, 12b and 12c formed in the base plate 4 and the manifold plates 6 and 7, respectively. .

  In this embodiment, the flow path unit 1 is configured by stacking five plates 3, 4, 6, 7, 9, and the manifolds 6 a, 7 a, 6 b, 7 b are connected to the manifold plates 6, 7. The pressure chamber 11 and the throttle portion 11b are formed on the cavity plate 3, and the nozzle 10 is formed on the nozzle plate 9, respectively. With such a configuration, the manifolds 6a, 7a, 6b, 7b, the pressure chamber 11, the nozzle 10, and the throttle portion 11b can be easily formed. In particular, the throttle portion 11b and the nozzle 10 having predetermined flow path resistances Ra and Rb are inexpensive. And can be formed efficiently.

  Particularly in the present embodiment, the narrowed portion 11b is formed by half etching on the same plate 3 on which the pressure chamber 11 is formed. Thereby, the narrowed portion 11b having a predetermined flow path resistance Ra can be formed more inexpensively and efficiently.

  Next, the actuator unit 2 will be described in detail with reference to FIG.

  The actuator unit 2 is formed by alternately laminating two piezoelectric sheets 21 and 23 having individual electrodes 28 formed on the surface and two piezoelectric sheets 22 and 24 having common electrodes 29 formed on the surface one by one. Further, a piezoelectric sheet 25 on which surface electrodes 26 and 27 (see FIG. 1) are formed is laminated thereon. These five piezoelectric sheets 21 to 25 constitute a piezoelectric element, and are both made of lead zirconate titanate (PZT) having ferroelectricity, and are slightly smaller than the channel unit 1 in plan view. It has a rectangular shape (see FIG. 1).

  As shown in FIG. 1, a large number of surface electrodes 26 are formed in a row along the longitudinal direction in the vicinity of both ends of the piezoelectric sheet 25 in the lateral direction. The surface electrode 27 is formed one by one on both ends in the longitudinal direction of each row of the surface electrodes 26.

  FIG. 4 shows only the individual electrodes 28 corresponding to the front surface electrodes 26 in the front side of FIG. 1, but as in the case of the front surface electrodes 26, both ends of the piezoelectric sheets 21 and 23 in the short direction. In the vicinity, a large number are formed in a row along the longitudinal direction (the vertical direction in FIG. 4). More specifically, the individual electrode 28 extends to the vicinity of the center in the short direction of the piezoelectric sheets 21 and 23 so as to face each pressure chamber 11 (see FIG. 4).

  The common electrode 29 is formed on almost the entire surface of the piezoelectric sheets 22 and 24 so as to include a region facing all the pressure chambers 11.

  As shown in FIG. 4, the two individual electrodes 28 that are vertically opposed to each other on the surfaces of the two piezoelectric sheets 21, 23 have through holes 30 formed in the piezoelectric sheets 22, 23, 24, 25 other than the lowermost layer. And the corresponding surface electrodes 26 on the piezoelectric sheet 25 are electrically connected to each other. Further, the two common electrodes 29 facing vertically on the surfaces of the two piezoelectric sheets 22 and 24 are passed through through holes (not shown) formed in the three layers of piezoelectric sheets 23, 24 and 25 from above. The electrode is electrically connected to the surface electrode 27 (see FIG. 1) on the piezoelectric sheet 25.

  Each surface electrode 26, 27 is connected to a controller (not shown) via the FPC 40, and the surface electrode 26 is independently controlled in potential, whereas the surface electrode 27 is always held at the ground potential. Thus, the individual electrodes 28 connected to the surface electrode 26 are independently controlled in potential, and the common electrode 29 connected to the surface electrode 27 is always held at the ground potential.

  The piezoelectric sheets 21 to 25 are polarized in the thickness direction, and are sandwiched between the individual electrodes 28 and the common electrode 29 in the three piezoelectric sheets 22, 23, and 24 excluding the lowermost layer and the uppermost layer piezoelectric sheets 21 and 25. The active part acts as the active part. In this case, when an electric field is applied in the polarization direction to the active portions of the piezoelectric sheets 22, 23, and 24 by setting the individual electrode 28 to a potential different from that of the common electrode 29, the active portions expand or contract in the thickness direction. Shrink or stretch in the surface direction due to the piezoelectric transverse effect. On the other hand, the lowermost and uppermost piezoelectric sheets 21 and 25 are inactive layers having no portion sandwiched between the individual electrode 28 and the common electrode 29 and cannot be spontaneously deformed.

  In the present embodiment, it is assumed that a drive pulse having a rectangular waveform as shown in FIG.

  In the drive pulse shown in FIG. 5A, the voltage is 0 in the range of times (i) and (iii), and is the voltage E1 in the range of time (ii). The time T1 of (ii) is the pulse width of the driving pulse, and T1 = T0 (T0: time for the pressure wave to propagate one way along the longitudinal direction of the pressure chamber 11).

  Here, the state change of the actuator unit 2 due to the application of the drive pulse will be described.

  First, before applying the drive pulse (time (i) in FIG. 5A), all the individual electrodes 28 are held at the ground potential in the same manner as the common electrode 29. At this time, the piezoelectric sheets 21 to 25 are almost flat as shown in FIG. 4 in all regions, and no ink meniscus protrudes or ink is ejected from the tip of each nozzle 10.

  Thereafter, at an appropriate timing, a drive pulse is applied to the individual electrode 28 corresponding to the pressure chamber 11 where the ink ejection operation is to be performed (time (ii) in FIG. 5A). At this time, the individual electrode 28 is at the voltage E1, and the piezoelectric sheets 21 to 25 corresponding to the individual electrode 28 are deformed so as to protrude to the opposite side (that is, upward) from the pressure chamber 11 as a whole. As a result, the volume of the pressure chamber 11 on the lower side is increased compared to the time (i), and negative pressure waves traveling toward the manifolds 6a, 7a, 6b and 7b are generated in the pressure chamber 11 and Ink is sucked into the pressure chamber 11 from the manifolds 6a, 7a, 6b, 7b.

  The application of the drive pulse is maintained for a time T1, and then the individual electrode 28 returns to the potential 0 again (time (iii) in FIG. 5A). At this time, like the time (i), all the individual electrodes 28 are held at the ground potential like the common electrode 29, and the piezoelectric sheets 21 to 25 are almost flat in the entire region.

  At the end of the application of the drive pulse (at the boundary between time (ii) and (iii) in FIG. 5), the volume of the pressure chamber 11 suddenly changes from the increased state to the original state. A positive pressure wave traveling toward the nozzle 10 is generated. The positive pressure wave is generated when the negative pressure wave previously generated by the application of the drive pulse is the end of the ink channel in the channel unit 1 (in this embodiment, the end of the throttle unit 11b shown in FIG. 4 on the side of the pressure chamber 11). Part) and is reflected by the reflection and becomes a positive pressure wave. By superposing the pressure waves in this way, a strong pressure is applied to the ink in the pressure chamber 11, and the ink is ejected from the end of the pressure chamber 11 through the holes 12 a, 12 b, and 12 c and from the tip of the nozzle 10.

  Note that the driving pulse shown in FIG. 5A corresponds to one ink droplet, and the inkjet head 101 ejects one ink droplet to one dot by applying the driving pulse, In order to perform gradation printing, it is possible to eject a plurality (for example, 2 to 4) of ink droplets for one dot. FIG. 5B shows a case where four ink droplets are ejected with respect to one dot, and four drive pulses are continuously applied to the actuator unit 2.

[Example]
In order to examine the effect of the inkjet head according to the present invention, various parameters such as the configuration of the ink flow path in the flow path unit 1, the frequency of the drive pulse applied to the actuator unit 2, and the temperature environment in which the head is used are changed. The experiment was conducted.

  About temperature environment, it was 5-45 degreeC and it changed 5 degreeC at a time. Table 1 shows the viscosity μ of the ink under each temperature condition.

  For the pressure chamber 11, the width b and the height h (see FIG. 6) are unified to 250 μm and 40 μm, respectively, and the flow path length l is changed to 1460 μm, 1960 μm, and 2460 μm, respectively, and the types (i) and (ii) (Iii). Table 2 shows the flow path resistance R in each type (i) (ii) (iii) of the pressure chamber.

  The channel resistance R was calculated from the following formulas (1) and (2) (where ΔP: pressure loss, Q: flow rate, r: equivalent radius). Equation (2) is based on the so-called “Poiseuille's Law”. As an example, Table 2 shows the channel resistance R when the temperature is 20 ° C. (that is, when the viscosity of the ink is μ = 3.2 cps, see Table 1). The same applies to Table 5.

  The ink flow path from the pressure chamber 11 to the nozzle 10 (see FIG. 4), that is, the ink flow path formed by the holes 12a, 12b, 12c of the plates 4, 6, 7 (pressure chamber-nozzle communication path) ), The channel length l was changed by changing the plate thickness. Table 3 shows the flow path resistance R in each type (i) (ii) (iii) of the pressure chamber-nozzle communication passage.

  For the nozzle 10, as shown in FIG. 7, the taper angle θ and the flow path length 1 (thickness of the plate 9) are unified to 8 ° and 75 μm, respectively, and the diameter d of the discharge port is changed to change the type ( i) (ii) (iii) (iv) (v). Table 4 shows the discharge port diameter d and the channel resistance Rb in each of the nozzle types (i) to (v).

  As for the throttle part 11b, as shown in FIGS. 8A and 8B, the flow path length l is unified to 550 μm, and the width b and the height h are changed while maintaining a certain relationship with each other. Table 5 shows the width b / height h and the channel resistance Ra in each type (i) to (iv) of the throttle portion.

  As shown in FIG. 5, the waveform of the drive pulse applied to the actuator unit 2 was set to pulse width T1 = T0 (T0: time during which the pressure wave propagates along the longitudinal direction of the pressure chamber 11). The voltage E1 was set to a value at which the ink ejection speed was 9 m / s at each temperature, and the frequency was changed in the range of 5 to 96 kHz.

  As described above, each element of the ink flow path in the flow path unit 1 is typed so that the flow path resistance R is different, and the ejection stability of each head formed by a combination of these types is examined. Table 6 shows, as an example, experimental results regarding combinations of the pressure chamber type (i) and the pressure chamber-nozzle communication passage type (i). In the table, “unstable” means that the ink is ejected in the form of a mist (that is, in multiple directions including directions other than the desired ejection direction), the ejection speed is extremely low, or ejection is impossible. .

  From Table 6, it can be seen that ◯ (temperature 5 to 45 ° C./stable in all cases of the drive pulse frequencies 24, 12, and 6 kHz) is distributed in a band shape. That is, it can be seen that the configuration of the restricting portion and the nozzle is greatly related to the discharge stability. Here, Table 7 shows the ratio Ra / Rb between the flow path resistance Ra of the throttle portion and the flow path resistance Rb of the nozzle corresponding to each case.

  From Table 7, in this example (combination of pressure chamber type (i) and pressure chamber-nozzle communication passage type (i)), the ratio between the flow path resistance Ra of the throttle portion and the flow path resistance Rb of the nozzle It can be seen that, when Ra / Rb is 0.48 to 1.26, stable ejection can be realized in the frequency range of the driving pulse and the temperature environment in which the head is used within the predetermined range.

  Further, in Table 8 and FIG. 9, in each case of the frequency of the drive pulse arbitrarily changed in the range of 5 to 96 kHz, the flow path resistance Ra of the throttle portion and the flow path resistance Rb of the nozzle that can realize stable ejection The upper and lower limits of the ratio Ra / Rb are shown.

  From Table 8 and FIG. 9, it can be seen that when the frequency of the drive pulse is 12 kHz, the upper and lower limits of Ra / Rb are the lowest value (0.48) and the highest value (1.26), respectively.

  Tables 6 to 8 and FIG. 9 show data related to the combination of the pressure chamber type (i) and the pressure chamber-nozzle communication passage type (i). Almost the same data was obtained for the combinations. That is, in all combinations of the pressure chamber types (i) to (iii) and the communication passage types (i) to (iii), the Ra / Rb values capable of realizing stable discharge were almost the same.

  From the above experimental results, by setting the ratio of the flow path resistance Ra of the throttle portion 11b to the flow path resistance Rb of the nozzle 10 to 0.48 to 1.26, the frequency of the drive pulse applied to the actuator unit 2 It was found that stable ejection can be realized even if the temperature environment in which the head is used is various. Furthermore, Ra / Rb is set to 0.63 to 1 from the viewpoint that it is possible to maintain good discharge stability even if a design error occurs, the temperature is outside the set temperature for use, or various other inconveniences occur. 05 is preferable, and 0.8 to 1.0 is more preferable.

  The reason why the ejection stability is impaired when Ra / Rb is outside the predetermined range is that the balance between the supply of ink to the pressure chamber 11 via the throttle portion 11b and the ejection of ink from the nozzle 10 is lost. It is assumed that this is the cause. More specifically, the following phenomenon is considered to occur. The amount of ink supplied from the manifolds 6a, 7a, 6b and 7b into the pressure chamber 11 via the throttle portion 11b is insufficient when Ra / Rb exceeds the upper limit value 1.26, and conversely Ra / Rb. Is below the lower limit of 0.48. When the ink supply into the pressure chamber 11 is excessive, the meniscus formed at the tip of the nozzle 10 protrudes too much, and a disadvantage such as excessive ink being ejected in a mist form may occur. On the other hand, when the ink supply into the pressure chamber 11 is insufficient, the meniscus is drawn into the nozzle 10 and excess air is drawn into the pressure chamber 11, so that the pressure required for ejection becomes the air. By being absorbed in the ink, there may be inconveniences such as the ink ejection speed being remarkably lowered or ejection impossible.

  The preferred embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and various design changes can be made as long as they are described in the claims. It is a thing. That is, the present invention is arranged on the ink chamber for containing ink, the pressure chamber to which ink is supplied from the ink chamber, and the pressure chamber, and is deformed by the application of the drive pulse to change the volume of the pressure chamber. The piezoelectric element is arranged between the ink chamber and the pressure chamber, communicates with the throttle portion having a narrower flow path than the pressure chamber, and the pressure chamber. The present invention is not limited to the above-described embodiment, and can be applied to various other configurations of inkjet heads. For example, the following modifications can be considered.

  The narrowed portion 11b may not be formed by half etching.

  The flow path unit 1 of the head does not have to be configured by laminating plates 3, 4, 6, 7, and 9, which are plate-shaped materials. For example, a space that forms an ink flow path in a single solid (that is, , A space including an ink chamber, a pressure chamber, a throttle portion, and a nozzle).

  The shape and size of the ink flow path formed in the head can be variously changed such that the nozzle 10 is not tapered (θ = 0).

  The material of the uppermost piezoelectric sheet 25 is not a PZT having ferroelectricity but a material having a low dielectric constant or insulating property from the viewpoint that unnecessary displacement does not occur even when a voltage is applied to the surface electrodes 26 and 27. It may consist of However, from the viewpoint that it can be integrally formed, it is preferably made of the same PZT as the other piezoelectric sheets 21 to 24.

  The waveform of the drive pulse applied to the actuator unit 2 may be upside down as illustrated in FIGS. 5 (a) and 5 (b).

  Regarding the driving method of the actuator unit 2 related to ink ejection, as described above, the piezoelectric sheet is made flat in a normal state, and the active portion of the piezoelectric sheet is deformed so as to protrude to the opposite side of the pressure chamber in response to the application of the driving pulse. Thereafter, the present invention is not limited to ejecting ink by returning the sheet to a flat state. For example, in a normal state, the piezoelectric sheet is flattened, and the active portion of the piezoelectric sheet is convexly deformed toward the pressure chamber in response to the application of the drive pulse, thereby reducing the volume of the pressure chamber and discharging the ink, and then flattening the sheet Or by supplying ink into the pressure chamber, or by normally deforming the active portion of the piezoelectric sheet convexly toward the pressure chamber, and flattening the piezoelectric sheet in response to the application of the drive pulse. Then, the method may be employed in which the volume of the pressure chamber is reduced to the original and the ink is ejected by deforming the active portion so as to protrude toward the pressure chamber again.

  The frequency of the drive pulse is not limited to 5 to 96 kHz.

  In the above-described embodiment, the potential of the common electrode is always 0 (V), but the present invention is not limited to this.

In the above-described embodiment, the pressure wave is applied to the ink in the pressure chamber 11 by the actuator unit 2 made of a piezoelectric element. However, the invention is not limited to this, and the electro-thermal conversion element or the electrostatic actuator is not limited thereto. You may make it give a pressure wave by.
Further, the ink jet head of the present invention is not limited to a printer, and can also be applied to an ink jet facsimile and a copier.

1 is an exploded perspective view of an inkjet head according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of a flow path unit included in the inkjet head shown in FIG. 1. FIG. 3 is a partially enlarged perspective view of the flow path unit shown in FIG. 2. FIG. 4 is a sectional view taken along line IV-IV in FIG. 1. It is the schematic which shows the drive pulse supplied to an actuator unit, (a) shows the case where one ink droplet is discharged, (b) shows the case where four ink droplets are discharged. It is the schematic which shows the space shape of a pressure chamber. It is sectional drawing which shows the nozzle formed in the nozzle plate. (A) is the elements on larger scale of the diaphragm part vicinity in FIG. (B) is sectional drawing along the BB line of (a). The upper limit of the ratio Ra / Rb between the flow path resistance Ra of the restrictor and the flow path resistance Rb of the nozzle that can realize stable ejection in each case of the frequency of the drive pulse arbitrarily changed in the range of 5 to 96 kHz, and It is a graph which shows a minimum.

Explanation of symbols

1 Flow path unit 2 Actuator unit 3 Cavity plate (plate material)
4 Base plate (plate material)
6,7 Manifold plate (plate material)
6a, 7a, 6b, 7b Manifold (ink chamber)
9 Nozzle plate (plate material)
DESCRIPTION OF SYMBOLS 10 Nozzle 11 Pressure chamber 11b Restriction part 21, 22, 23, 24, 25 Piezoelectric sheet (piezoelectric element)
28 Individual Electrode 29 Common Electrode 40 Flexible Printed Circuit Board 101 Inkjet Head

Claims (8)

An ink chamber for containing ink;
A pressure chamber to which ink is supplied from the ink chamber;
A pressure applying means disposed on the pressure chamber, and applying pressure fluctuation to the ink in the pressure chamber by application of a driving pulse;
A throttle portion disposed between the ink chamber and the pressure chamber, and having a narrower flow path than the pressure chamber;
A nozzle that communicates with the pressure chamber and ejects ink in accordance with a change in volume of the pressure chamber;
The inkjet head according to claim 1, wherein a ratio Ra / Rb of the flow path resistance Ra of the narrowed portion and the flow path resistance Rb of the nozzle is 0.48 to 1.26.   The inkjet head according to claim 1, wherein the pressure applying unit is a piezoelectric element that is deformed by application of the drive pulse to change a volume of the pressure chamber.   The piezoelectric element is deformed so as to increase the volume of the pressure chamber when the drive pulse is applied, and is deformed so that the volume of the pressure chamber is restored when the drive pulse is applied. Item 3. The inkjet head according to Item 2.   4. The ratio Ra / Rb between the flow path resistance Ra of the narrowed portion and the flow path resistance Rb of the nozzle is 0.8 to 1.0, according to claim 1. Inkjet head.   The inkjet head according to any one of claims 1 to 4, wherein a frequency of the driving pulse is 5 to 96 kHz.   The inkjet head according to claim 1, wherein the narrowed portion is formed by half etching. It is composed by laminating a plurality of plate-like materials,
The inkjet head according to claim 1, wherein the ink chamber, the pressure chamber, the throttle portion, and the nozzle are formed in any of the plurality of plate-like materials. . The inkjet head according to claim 7, wherein the narrowed portion is formed by half etching on the same plate-like material on which the pressure chamber is formed.

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